Methods, systems and/or apparatus relating to steam turbine exhaust diffusers

ABSTRACT

An axial flow steam turbine flow path that includes a rotor and a casing defining the axial steam flow path; and a toroidal diffuser for diffusing the exhaust steam and turning the exhaust steam from a generally axial flow direction to a generally transverse or vertical and tangential direction; wherein the toroidal diffuser comprises a diffuser that, at least in part, incorporates the shape of a toroid or a section of a toroid; and wherein a toroid comprises the shape generated by revolving a circular or oval shape in three dimensional space about an axis coplanar with the circular or oval shape, which does not touch the circular or oval shape.

BACKGROUND OF THE INVENTION

This present application relates generally to methods, systems, and/or apparatus for improving the efficiency and/or operation of turbine engines. More specifically, but not by way of limitation, the present application relates to methods, systems, and/or apparatus pertaining to improved steam turbine diffusers and related components.

In conventional steam turbine design, the inner case of the steam turbine, which, for example, may be a double flow down exhaust unit, has an encompassing exhaust hood split vertically and extending along opposite sides and ends of the turbine. This large box-like structure houses the entire low pressure section of the turbine. The exhaust steam from the turbine flows downstream in a general axial direction. Then, the steam exhaust is redirected from an axial flow direction to a flow direction 90° relative to the axial flow direction. This 90° flow direction may be in any plane, downwardly, upwardly or transversely.

Generally, conventional exhaust hoods for steam turbines constitute large rectilinear structures at the exit end of the conical section for turning and diffusing the steam flow at right angles. The steam flow path was thus somewhat tortuous, which resulted in losses and adverse pressure drop. It will also be appreciated that access to various parts of the turbine, for example, the bearing for maintenance purposes was difficult in that it could necessitate the removal of the upper half of the exhaust hood. Further, it will be appreciated that the exhaust hood in conventional steam turbines typically supports the inner casing of the turbine and the associated steam path parts such as diaphragms and the like. Accordingly, there has been found a need to provide a new geometry to improve exhaust steam pressure recovery and overall performance of the turbine.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes an axial flow steam turbine flow path that includes a rotor and a casing defining the axial steam flow path; and a toroidal diffuser for diffusing the exhaust steam and turning the exhaust steam from a generally axial flow direction to a generally transverse or vertical and tangential direction; wherein the toroidal diffuser comprises a diffuser that, at least in part, incorporates the shape of a toroid or a section of a toroid; and wherein a toroid comprises the shape generated by revolving a circular or oval shape in three dimensional space about an axis coplanar with the circular or oval shape, which does not touch the circular or oval shape.

These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in con junction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional illustration of approximately half of a double flow down exhaust steam turbine according to conventional design;

FIG. 2 is a schematic side cross-sectional view of approximately half of a steam turbine illustrating an exhaust diffuser having a toroidal configuration according to an exemplary embodiment of the present application;

FIG. 3 is a schematic cross-sectional view from a downstream perspective of an exhaust diffuser having a toroidal configuration according to an exemplary embodiment of the present application; and

FIG. 4 is an exemplary toroid shape from which diffusers according to the present application may the formed.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, particularly to FIG. 1 there is illustrated a portion of a steam turbine, generally designated 10, that includes a rotor 12 that mounts a plurality of turbine buckets 14. An inner casing 16 is also illustrated mounting a plurality of diaphragms or stator blades 18. A centrally disposed generally radial steam inlet 20 applies steam to each of the turbine buckets 14 and stator blades 18 on opposite axial sides of the turbine to drive the rotor 12. The stator vanes of the diaphragms 18 and the axially adjacent buckets 14 form the various stages of the turbine 10 and a flow path therethrough. It will be appreciated that the steam is exhausted from the final stage of the turbine for flow through a diffuser and into a condenser not shown.

Also illustrated in FIG. 1 is an outer exhaust hood 22 that surrounds and supports the inner casing 16 of the turbine 10 as well as other parts such as the bearings. In the illustration of FIG. 1, the turbine 10 includes steam guides 24 for directing the steam exhausting from the turbine 10 into an outlet 26 for flow to one or more condensers (not shown). With the use of an exhaust hood 22 supporting the turbine 10, bearings and ancillary parts, the exhaust steam path, as illustrated, is tortuous and subject to pressure losses. As one of ordinary skill in the art will appreciate, this results in a reduction in performance and efficiency.

Referring now to FIGS. 2 and 3, there is illustrated an aspect of the present invention wherein like reference numerals as in FIG. 1 are applied to like parts preceded by the numeral “1”. As illustrated, the exhaust hood 22 of the prior art is completely eliminated in favor of an exemplary toroidal diffuser 40 according to the present invention. As used herein and as discussed in more detail below, a toroidal diffuser is a diffuser that, at least in part, incorporates the shape of a toroid or a section of a toroid. An exemplary toroid, a toroid 41, is illustrated in FIG. 4. As shown, a toroid is the shape generated by revolving a circle in three dimensional space about an axis coplanar with the circle, which does not touch the circle. Typically, a toroid includes a circular shape that is revolved; however, as used herein, a toroid may include approximate circular shapes, such as an oval.

According to a preferred embodiment, the toroidal diffuser 40 generally includes a conical guide 45, which functions as the initial guide for the steam as it exits the last turbine section, a toroidal section 42, which, as illustrated, defines the upper half of the main body or chamber of the diffuser, and a rectilinear section 43, which defines the lower half of the main body or chamber of the diffuser and provides the flow path to an outlet 46. The toroidal section 42 may comprise approximately one half of a toroid shape, though other configurations are also possible. The toroidal section 42 engages and transitions to the rectilinear section 43 at a circumferential location that is approximately horizontal with the rotor 112. The axis of the toroid that forms the toroidal section 42 generally is the rotor 112.

The toroidal diffuser 40 may include other components that allow it to function in a more efficient and cost-effective manner. In some preferred embodiments, as already described, the toroidal diffuser 40 may include the conical guide 45. The upstream end of the conical guide 45, as illustrated, may be coupled to the inner casing 116 by a flexible joint 44. The conical guide 45 generally provides the outer radial boundary for steam exiting the final stage of the turbine. As illustrated, the conical guide 45 generally includes an expanding conical shape that has an axis along the rotor 112. Accordingly, the conical guide 45 has an increasing cross-sectional area, which allows the exiting steam to expand and, thereby, reduce its pressure. Particularly, the conical guide 45 has a cross-sectional diameter that increases as the distance from the flexible joint 44 increases. The conical guide 45 extends downstream and terminates at a flared lip 47. The flared lip 47 helps to smooth the flow and lessen the pressure of the steam into the toroidal section 42. As illustrated, the conical guide 45 may extend into the toroidal section 42 and/or rectilinear section 43. More specifically, the conical guide 45 may extend across approximately half the axial width of the toroidal section 42 and/or the rectilinear section 43. According to preferred embodiments, the inner boundary for the steam moving through the conical guide 45 may be provided by a cylindrical formed rotor plate 49. The cylindrical rotor plate 49 generally forms a smooth cylindrical shape that encloses the rotor and extends axially from the last stage of the turbine to the downstream wall of the toroidal diffuser 40. The axis of the rotor plate 49 also may be the rotor 112.

It has been discovered that the geometry of the toroidal section 42, according to the present invention, is effective at allowing the exiting steam to expand and reduce its pressure. These benefits are further enhanced by the combination of the toroidal section 42 and the conical guide 45. The toroidal diffuser 40, with the toroidal section 42 and/or the conical guide 45, is also effective at guiding the diffused steam to the outlet 46 with a minimum pressure loss. It will be appreciated that the outlet 46 need not be a down exhaust but can be a side or upwardly directed exhaust.

Apart from the increased performance due to the diffusion of the steam in a toroid on the steam exhaust side of the turbine, there are additional advantages. For example, the exhaust hood in prior conventional steam turbines is eliminated and there is no longer a need to support the inner casing and associated steam path parts, such as diaphragms from the exhaust hood. Cost reduction is also realized because an exhaust hood is no longer used to enclose the inner casing. Steam guides previously necessary are also entirely eliminated. Importantly, the inner casing and the toroidal diffuser of the turbine are each supported directly from the foundation of the turbine. To facilitate this, a flexible connection 44 (FIG. 2) is provided between the inner casing and the toroidal diffuser 40. The flexible connection may be of many different types such as an expansion bellows to allow for differential thermal expansion. Further, the previously utilized exhaust hood is no longer necessary for the support of the turbine bearings. As illustrated in FIG. 2, the bearings 54 may be supported on stanchions 56 in turn directly supported by the foundation of the turbine. Thus, the stanchions provide a rigid support for the bearings with improved turbine reliability as a result. The toroid diffuser 40 may be formed of a composite material, steel plate or pipe, structural steel, fiber-reinforced plastic or any combination of these materials to obtain the required structural integrity and desired steam flow diffusion characteristics.

From the above description of preferred embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof. 

1. An axial flow steam turbine flow path comprising: a rotor and a casing defining the axial steam flow path; and a toroidal diffuser for diffusing the exhaust steam and turning the exhaust steam from a generally axial flow direction to a generally transverse or vertical and tangential direction.
 2. The flow path according to claim 1, wherein the toroidal diffuser comprises a diffuser that, at least in part, incorporates the shape of a toroid or a section of a toroid.
 3. The flow path according to claim 1, wherein a toroid comprises the shape generated by revolving a circular or oval shape in three dimensional space about an axis coplanar with the circular or oval shape, which does not touch the circular or oval shape.
 4. The flow path according to claim 3, wherein a toroid comprises the shape generated by revolving a circle in three dimensional space about an axis coplanar with the circle, which does not touch the circle.
 5. The flow path according to claim 1, wherein a toroidal diffuser comprises: a conical guide, which functions as the initial guide for the steam as it exits the last turbine section; a toroidal section, which defines the upper half of the main chamber of the toroidal diffuser; and a rectilinear section, which defines the lower half of the main chamber of the diffuser and provides a flow path to an outlet.
 6. The flow path according to claim 5, wherein the toroidal section comprises approximately one half of a toroid shape.
 7. The flow path according to claim 5, wherein the toroidal section engages the rectilinear section at a circumferential location that is approximately horizontal with the rotor.
 8. The flow path according to claim 5, wherein the axis of the toroid that forms the toroidal section comprises the rotor of the turbine.
 9. The flow path according to claim 5, wherein the upstream end of the conical guide is coupled to the casing by a flexible joint; and wherein the conical guide comprise an outer radial boundary for steam exiting a final stage of the turbine.
 10. The flow path according to claim 5, wherein the conical guide includes an expanding conical shape such that the cross-sectional diameter of the conical guide increases as the distance downstream from the flexible joint increases.
 11. The flow path according to claim 5, wherein at a downstream end the conical guide comprises a flared lip.
 12. The flow path according to claim 5, wherein the conical guide extends into the toroidal section and the rectilinear section.
 13. The flow path according to claim 12, wherein the conical guide extends across approximately half the axial width of the toroidal section and the rectilinear section.
 14. The flow path according to claim 5, wherein an inner boundary for the steam moving through the conical guide comprises a cylindrical rotor plate that is disposed around the rotor of the turbine, the cylindrical rotor plate comprising a smooth cylindrical shape that substantially encloses the rotor and extends axially from the last stage of the turbine to a downstream wall of the toroidal diffuser.
 15. The flow path according to claim 1, wherein the casing and the toroidal diffuser are independently mounted relative to one another on a foundation.
 16. The flow path according to claim 1, wherein a flexible connection connects the casing and the toroidal diffuser.
 17. The flow path according to claim 16, wherein the flexible connection comprises expansion bellows that are configured to allow for differential thermal expansion.
 18. The flow path according to claim 1, wherein bearings for the rotor are supported on one or more stanchions that are directly supported by the foundation of the turbine.
 19. An axial flow steam turbine flow path comprising: a rotor and a casing defining the axial steam flow path; and a toroidal diffuser for diffusing the exhaust steam and turning the exhaust steam from a generally axial flow direction to a generally transverse or vertical and tangential direction; wherein the toroidal diffuser comprises a diffuser that, at least in part, incorporates the shape of a toroid or a section of a toroid; and wherein a toroid comprises the shape generated by revolving a circular or oval shape in three dimensional space about an axis coplanar with the circular or oval shape, which does not touch the circular or oval shape.
 20. The flow path according to claim 19, wherein a toroidal diffuser comprises: a conical guide, which functions as the initial guide for the steam as it exits the last turbine section; a toroidal section, which defines the upper half of the main chamber of the toroidal diffuser; and a rectilinear section, which defines the lower half of the main chamber of the diffuser and provides a flow path to an outlet. 